wchar.rs should not import let alone reexport FFI strings.
Stop re-exporting utf32str! because we use L! instead.
In wchar_ffi.rs, stop re-exporting cxx::CxxWString because that hasn't
seen adoption.
I think we should use re-exports only for aliases like "wstr" or for aliases
into internal modules.
So I'd probably remove `pub use wchar_ffi::wcharz_t = crate::ffi::wcharz_t`
as well.
A following commit will pass global string constants to the gettext macro.
This is not ideal because we might accidentally use the constants without
gettext (which we should never do). To fix that we might need to define a
macro per constant, or use a proc macro which is maybe not worth it.